Smart consumers look for products and services that offer the best value for their money. Merchants for these products and services have payment services that typically accepts only U.S. Dollar (USD), European Euro (EUR) or other fiat money. This invention modernizes merchant payment services so that consumers have the flexibility to pay for fiat charges with fiat or Bitcoin (BTC), Ethereum (ETH), or other cryptocurrencies. The term “cryptocurrency” in this invention is in common parlance with: “virtual currency,” “digital money,” “digital currency,” “digital asset,” “internet money,” “electronic coin,” “electronic cash,” “peer-to-peer electronic cash,” “unspent output,” “unspent transaction output,” and “UTXO.” With this invention, consumers can use Flexible fiat and cryptocurrency Payment Services (FfcPS) to use money that has the best value at time of payment. For an example of money with best value, consider a consumer that purchased one BTC at $500 (500 USD) and wants to use that BTC when it's value is more than $500 at time of payment for a product or service, and would otherwise use USD.